1. The Field of the Invention
The present invention relates to impeller assemblies used with fluid processing systems such as bioreactors and fermentors.
2. The Relevant Technology
The biopharmaceutical industry uses a broad range of mixing systems for a variety of processes such as in the preparation of media and buffers and in the growing, mixing and suspension of cells and microorganisms. Some conventional mixing systems, including bioreactors and fermentors, comprise a flexible bag disposed within a rigid support housing. An impeller is disposed within the flexible bag and is coupled with a drive shaft projecting into the bag. Rotation of the drive shaft and impeller facilitates mixing and/or suspension of the fluid contained within flexible bag.
Although the current mixing systems are useful, they have some limitations. For example, where the drive shaft is secured within the flexible bag during the manufacturing process, the rigid drive shaft limits the ability to collapse or fold the flexible bag so as to reduce its size for transportation, storage and/or further processing. Likewise, where it is intended to reuse the drive shaft, such as when it is made of metal, this system has the disadvantage of needing to clean and sterilize the drive shaft between different uses.
In an alternative mixing system, a flexible tube is disposed within a flexible bag. A first end of the tube is rotatably coupled by a dynamic seal to the bag while an opposing second end of the tube is sealed to an impeller. During use, a rigid drive shaft is passed down into the tube and couples with the impeller. In turn, rotation of the drive shaft facilitates rotation of the tube and impeller for mixing the fluid within the flexible bag. In this design, before the drive shaft is inserted, the combined flexible bag and tube can be folded for ease of storage and transportation. In addition, the tube isolates the drive shaft from the fluid so that during use the drive shaft does not directly contact the fluid within the bag. As such, following use, the drive shaft can be removed and reused without the need for cleaning or sterilization.
Although the mixing system using the flexible tube has a number of improved advantages, it also has some limitations. For example, the flexible tube design is limited to a single impeller mounted on the end thereof. In larger volume mixing systems or in applications where higher rates of mixing are required, a single impeller may not be sufficient to achieve a needed mixing rate. Accordingly, what is needed in the art are mixing systems that retain all or some of the advantages of using the flexible tube to isolate the rigid drive shaft from the fluid but enable higher mixing rates relative to the single impeller design.